Why Raspberry Pi Pico (RP2040) is replacing Arduino Leonardo for hardware mouse control:

1. Dual Cortex-M0+ cores running at 133MHz (5x faster than 16MHz ATmega32U4).
2. Hardware USB Controller supports custom TinyUSB HID descriptors.
3. UART / Serial baud rate supports up to 921,600 baud, reducing serial packet latency from 4ms down to 0.1ms.

Code snippet in C with TinyUSB:

#include "tusb.h"
void send_mouse_delta(int8_t dx, int8_t dy, uint8_t buttons) {
    if (tud_hid_ready()) {
        tud_hid_mouse_report(0, buttons, dx, dy, 0, 0);
    }
}

RP2040 is awesome. You can also spoof the USB string descriptors (Manufacturer, Product, Serial) in flash memory.

0.1ms transfer latency is huge. Completely eliminates input delay on fast flicks.